gzumwalt Dual Mode Windup Car Remix

This is a complete remix of the awesome Dual Mode Windup Car by Greg Zumwalt, which is no longer on thingiverse, but which you can find here: https://www.myminifactory.com/object/3d-print-dual-mode-windup-car-27061

One of my childhood favorite toys was a model of Herbie, the love bug. So I wanted to draw a remix that reminded me of it, although later I followed the New Beetle design more closely.

Greg rightly notes in his comments that weight has a lot of influence on the performance of this toy. I noticed this with the first heavy prototype.

I then redesigned the gears set, enlarging them to accommodate a bigger and more powerful spring.

Initially, both for greater smoothness and to improve mechanical tolerances, I created a model that includes 10 ball bearings: no. 5 10x15x4mm (6700ZZ) and no.5 6x12x4mm (MR126ZZ). You can conveniently replace the latters by properly cutting Igus Iglidur 6x12 bushes as you can see in one of the attached pictures.
But I realized that the bearings on the wheel axles were not as sliding as the plastic bushings.
So, although the drawing remained the one to use the bearings, I designed bushings to eliminate the bearings.
To those who object that this increases the number of pieces and complications, I reply by saying that bushes wear out over time and that it is better to reprint simple bushes rather than a side body with worn holes. I get the best results by printing the bushings with PET, which is perhaps the best material also for printing the spring.

Another complication with respect to the original design is that it is necessary to thread several holes (M3), those on the wheel axles and those of the three spacers that hold the side bodies together. But thanks to these screwed spacers, a strict tolerance on cross members is no longer necessary.

To avoid collisions with the rims, M3 round head screws should be used in order to tighten the spacers to the body.

I designed a different rim, with a central locking screw: any M3 screw can be used to lock the rims to the axles.
For the tires I was inspired by John Corkery's remix, published here: https://www.thingiverse.com/thing:2140611. I designed the tire with a more curved profile, to reduce the footprint and reduce friction. Better to use a soft flexible filament to print the tires because the high initial power combined with the weight of the model could cause the tires to slip on very smooth surfaces.

For those wondering what is the reason for the strange design of the recharge key, I did it to be able to insert it under the body top during transport, as seen in one of the attached photos.

Finally, I included step files for all the elements you might want to change according to the output of your printer.

I did not count the hours needed to print the model, but we should be on time to have it ready for Christmas gifts.

[EDIT 11/29/2019]

rim_2_x_4.stl added: symmetricalò rim with more internal clearance.
rim_2-or_x_4.stl added: as above, but suitable for o-rings as tire. For the o-ring measure please refer to the instructions on the gzumwalt original project page on myminifactory.

[EDIT 12/01/2019]
Detailed body stl and step added. It's a body variant with separated beam, rear and turn lights, handles and license plates. Some components may need to be glued.
The license plates are clear: you can customize them with post-processing, or modify the step files to extrude the characters, to be printed with different colors.
All files concerning the detailed body have the DB prefix.

[EDIT 12/10/2019]
UL_DB_NB_body_left.stl and UL_DB_NB_body_right.stl added. They are the hollow version of the side detailed bodies. This print needs supports. It has saved over 40 grams in my print using ABS.